In the fabrication of semiconductor integrated circuits, metal conductor lines are used to interconnect the multiple components in device circuits on a semiconductor wafer. A general process used in the deposition of metal conductor line patterns on semiconductor wafers includes deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal conductor line pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked conductor line pattern; and removing the mask layer typically using reactive plasma and chlorine gas, thereby exposing the top surface of the metal conductor lines. Typically, multiple alternating layers of electrically conductive and insulative materials are sequentially deposited on the wafer substrate, and conductive layers at different levels on the wafer may be electrically connected to each other by etching vias, or openings, in the insulative layers and filling the vias using aluminum, tungsten or other metal to establish electrical connection between the conductive layers.
A current drive in the semiconductor device industry is to produce semiconductors having an increasingly large density of integrated circuits which are ever-decreasing in size. These goals are achieved by scaling down the size of the circuit features in both the lateral and vertical dimensions. Vertical downscaling requires that the thickness of gate oxides on the wafer be reduced by a degree which corresponds to shrinkage of the circuit features in the lateral dimension. While there are still circumstances in which thicker gate dielectrics on a wafer are useful, such as to maintain operating voltage compatibility between the device circuits manufactured on a wafer and the current packaged integrated circuits which operate at a standard voltage, ultrathin gate dielectrics will become increasingly essential for the fabrication of semiconductor integrated circuits in the burgeoning small/fast device technology.
The ongoing advances in the field of fabricating miniaturized electronic integrated circuits (ICs) has involved the fabrication of multiple layers of interconnects, or the layers of separate electrical conductors which are formed on top of a substrate and connect various functional components of the substrate and other electrical connections to the IC. Electrical connections between the interconnect layers and the functional components on the substrate are achieved by via interconnects, which are post- or plug-like vertical connections between the conductors of the interconnect layers and the substrate. ICs often have five or more interconnect layers formed on top of the substrate.
Only a relatively short time ago, it was impossible or very difficult to construct an IC with more than one or two layers of interconnects. The topology variations created by forming multiple layers on top of one another resulted in such significant depth of focus problems with lithographic processes that any further additions of layers were nearly impossible to achieve. However, recent advances in semiconductor fabrication planarization techniques, such as chemical mechanical polishing (CMP), have been successful in smoothing relatively significant variations in the height or topography of each interconnect layer. As a result of the smoothing, or planarization, conventional lithographic processes are repetitively used without significant limitation to form considerably more layers of interconnects than had previously been possible.
The multiple interconnect layers occupy volume within the IC, although they do not necessarily occupy additional substrate surface area. Nevertheless, because surface area and volume are critical considerations in Ics, attention has been focused on the effective use of the space between the interconnect layers. Normally, the space between the interconnect layers is occupied by an insulating material, known as an interlayer dielectric (ILD) or intermetal dielectric (IMD), to insulate the electrical signals conducted by the various conductors of the interconnect layers from each other and from the functional components in the underlying substrate.
One effective use for the space between the interconnect layers is the incorporation of capacitors between the interconnect layers in the IMD insulating material separating the interconnect layers. These capacitors form part of the functional components of the IC. Previously, capacitors were constructed in the first layers of IC fabrication immediately above the substrate alongside other structures, such as transistors, so the capacitors were formed of generally the same material used to construct the other functional components, such as polysilicon. Capacitors formed of these materials are generally known as poly-plate capacitors.
Because the conductors of the interconnect layers are metal in construction, the capacitors formed between the interconnect layers are preferably of a metal-insulator-metal (MIM) construction to take advantage of processing steps and performance enhancements. MIM capacitors are very valuable in many applications of semiconductor technology. For example, MIMs can be used in RF circuits, analog ICs, high power microprocessor units (MPUs), and DRAM cells. An MIM capacitor has metal plates which are usually formed on the metal conductors of the interconnect layers. Because metal fabrication is required for the conductors of the interconnect layers, the simultaneous or near-simultaneous formation of the metal capacitor plates is readily accomplished without significant additional process steps and manufacturing costs.
A typical process flow for MIM capacitor fabrication includes crown capacitor patterning, bottom electrode deposition, bottom electrode CMP (chemical mechanical planarization), dielectric layer deposition, and top electrode deposition and patterning. Normally, dielectric materials having a high dielectric constant (k) are used as the insulating dielectric layer between the electrodes. The dielectric layer is typically a thin (<100 angstroms in thickness) low-k dielectric film in order to achieve a low EOT (equivalent oxide thickness), which corresponds to a high capacitance.
The electrodes of an MIM capacitor are fabricated using metals such as TiN, TaN, WN, etc., which are deposited using CVD (chemical vapor deposition) or ALD (atomic layer deposition) methods. Generally, due to their compatibility to semiconductor fabrication processes, MOCVD (metal organic chemical vapor deposition) films are used as electrode materials. MIM capacitors used for logic-friendly embedded DRAM features require a low-temperature electrode deposition process (typically less than about 500 degrees C.).
Due to the typically extremely small thickness of the dielectric layer, formation of an interfacial layer between the dielectric layer and the bottom electrode, as well as between the dielectric layer and the top electrode, significantly impacts EOT scaling down in the effort to achieve ever-decreasing capacitances. Top electrode interaction with thin, high-k dielectric materials has been found to adversely impact the electrical performance of MIM capacitors, including excessive junction leakage and lower breakdown voltage. Recent research indicates that the electrical performance of MIM capacitors is strongly correlated with plasma damage induced in the dielectric layer during deposition of the top electrode on the dielectric layer. This is particularly problematic with regard to dielectric layers which are fabricated using high-k dielectric materials. Accordingly, a new and improved electrode fabrication method is needed to reduce the formation of an interfacial layer between a dielectric layer and an electrode, as well as prevent plasma-induced damage to the dielectric layer during electrode layer deposition, during the fabrication of an MIM capacitor on a substrate.
An object of the present invention is to provide a novel method of forming MIM capacitor electrodes.
Another object of the present invention is to provide a novel method of forming electrodes of an MIM capacitor to enhance the electrical performance characteristics of the capacitor.
Still another object of the present invention is to provide a novel MIM capacitor electrode fabrication method which reduces the formation of interfacial layers in an MIM capacitor.
Yet another object of the present invention is to provide a novel MIM capacitor electrode fabrication method which improves MIM capacitor performance by preventing plasma-induced damage to a dielectric layer during deposition of a top electrode on the dielectric layer in fabrication of the MIM capacitor.
A still further object of the present invention is to provide a novel MIM capacitor electrode fabrication method which includes patterning of crown-type capacitor openings in a substrate; deposition of a bottom electrode in each of the capacitor openings; rapid thermal processing (RTP) or thermal annealing of the bottom electrode; deposition of a dielectric layer on the bottom electrode; plasma-free deposition of a top electrode on the dielectric layer; and patterning of the top electrode.